Wireless communication system with detectors for extraneous received signals

ABSTRACT

A wireless communication system having base stations, remotely located terminal units and a base station controller. The base stations and the remotely located terminal units communicate data over operational wireless communication links between them. The base stations include respective in-channel detectors and out-of-channel detectors for detecting radar or other extraneous received signals. The in-channel detectors analyse signals over the operational communication links. The out-of-channel detectors include respective out-of-channel receiver elements that monitor possibly available channels alternative to the respective operational communication link channels. The base station controller registers whether channels are available or not for communication links, and allocates to the base stations respective target channel parameters including frequencies available for operational and alternative communication links. The base stations store the respective target channel parameters for available operational and alternative communication links.

FIELD OF THE INVENTION

This invention relates to a wireless communication system with detectorsfor extraneous received signals.

Wireless communication refers to communication of data using modulatedelectromagnetic radiation through a non-solid medium. The term does notimply that the associated devices do not contain any wires. Wirelesscommunications may be utilized in conjunction with wired communications.

BACKGROUND OF THE INVENTION

Various techniques to allocate spectrum usage, in various dimensions,such as time, frequency, and the ability to combine/separate signals maybe employed to use limited spectrum bandwidth more efficiently, with aprotocol for sharing, allocating and reusing the spectrum bandwidth.

These protocols may also be designed with consideration for a number ofenvironmental factors, and may also be scalable given that theseprotocols are often used in conjunction with dynamic systems where thenumber of devices may vary over time, and communication needs may alsovary over time. For example, devices may enter the network, leave thenetwork, record data, send updates, receive configuration files, andreceive instructions. Further issues may include the density of thedevices within a physical area and the need for simultaneouscommunications.

Environmental factors may include, for example, issues with spectralnoise, interference, signal degradation, waveabsorption/blocking/reflection, multipath fading, and limitedavailability of spectrum.

Furthermore, in systems where there may be a large number of devices,the system may be designed, for example, to account for devices joiningand exiting the network, allocation and resizing of various transmissionpathways needed by various devices, broadcasting messages across anumber of devices, accounting for devices malfunctioning or otherwisebeing out of communication, and redundancy requirements.

Typically a radio (or wireless) local area network (RLAN) has one ormore base stations (or access points), a plurality of remotely locatedterminal units (or user equipment) transmitting and receiving data overoperational wireless communication links, and a base station controllerthat controls channel parameters used by the base stations for therespective communication links. The term base station is used herein torefer to a wireless communications station installed usually at a fixedlocation and used for wireless communication with terminal units, whichmay be mobile. The base stations may communicate also over wired orwireless communication links with other base stations and one or morebase station controllers. The terminal units may also communicatedirectly with each other in some configurations without thecommunication passing through a base station or a base stationcontroller.

Our Patent Specification GB2529029 describes use of RLANs in variousapplications. One such application is in an automatic or semi-automaticwarehouse facility with robots including RLAN communication terminalunits. Movements of the robots may be enabled across various paths, someof which may intersect. The warehouse facility may include bins arrangedfor example in a grid-like structure, where robots move to place objectsin and pick objects from the bins. The RLAN may also include othermobile, non-robot terminal units, for example communication terminalunits carried by human beings. The facility includes a robot controlsystem with real-time or near real-time wireless communication betweenthe robot control system, the base stations and the terminal units. Therobot control system controls the navigation/routing of robots,including, but not limited to, moving from one location to another,collision avoidance, optimization of movement paths, control ofactivities to be performed. The base station controller controlsparameters of the communication links, rather than the content of thecommunications.

Many other applications of the RLANs are described in PatentSpecification GB2529029, for example the terminal units collecting dataincluding operational data, performance data, analytic metrics relatedto operations of the system, storing and transmitting metrics regardingroute planning or obstacles on a map, such intelligence being processedat a base station, or a central server, and decisions distributed to theterminals on the network. Information gathered may be utilized to mapvarious properties of terminals over a period of time. For example, theflow of people using terminal units in the form of wearable devices,such as wristbands may be mapped as they move around a location, whichmay be useful for determining bottlenecks in the movement of people insubway stations, or the flow of people in a music festival or anexhibition space, for example. The terminals may be utilized to providevoting capabilities to one or more people and sent individually to thebase stations, and/or the votes aggregated together by various terminalsand then sent up in aggregate to the base stations. Voting may be usedin various contexts and applications, for example, voting at a gameshow, voting at a concert, voting for political parties.

There are various communication technologies/protocols available, suchas the IEEE 802.11/Wi-Fi™ standards, and wireless cellularcommunications (2G, 3G, Universal Mobile Telecommunications System(UMTS), Long-Term Evolution (LTE), for example. A challenge common tothe different technologies of wireless networks when providing effectiveand consistent communication is limited spectrum bandwidth. Spectrum islimited both by natural constraints such as interference bytransmissions from neighbouring devices or by noise and also bylegal/regulatory requirements. For example certain bands of frequencyare highly regulated and are allocated to, or prioritise particularuses. An example of such restrictions apply in the frequency range of5470-5725 MHz that permit unlicensed transmissions but require detectionand avoidance of interference with radar signals. Further, these RLANsmay use frequency bands that are also used by other types of devices forcommunications or other uses causing external traffic and noiseinterference, exacerbated by undesirable signal characteristics such asattenuation when penetrating walls or other solids, lack of bandwidth,low bit rate, antenna size, transmission power, and beam density.

In order to improve functioning, and in certain frequency ranges toensure compliance with regulatory requirements, RLANs can use techniquesof changing the channel parameters, especially the frequencies used forthe communication links. For this purpose, the RLAN system may includedetectors for detecting extraneous received signals such as interferenceby noise, or by signals (such as radar) to which compliance with theregulations requires reaction, and change the channel parametersincluding the frequencies to avoid the interference. One conventionaltechnique of detection of extraneous received signals and changing thechannel parameters including the frequencies is referred to as dynamicfrequency selection (DFS). Autonomous reaction by the different basestations would cause complications unless suitable precautions are takenfor allocation of the channel parameters used by the base stations forthe respective communication links. Moreover, if the transmissions areinterrupted or the interference of the receptions continues while thechannel parameters are changed, the time delay may be prohibitiveespecially if the procedure for checking and implementing the targetchannel parameters is prolonged.

A wireless communication system enabling prompt reaction to detection ofextraneous received signals with minimal disturbance to communicationlinks is desirable.

SUMMARY

Some embodiments of the present disclosure provide a wirelesscommunication system comprising a plurality of base stations, aplurality of remotely located terminal units and at least one basestation controller. The base stations and the remotely located terminalunits comprise respective communication modules for transmitting andreceiving data over operational wireless communication links between atleast the base stations and the terminal units. The communicationmodules include respective in-channel receiver elements for signalsreceived over the operational communication links. The base stationcontroller controls channel parameters used by the base stations for therespective communication links, the channel parameters includingallocations of frequencies for use in the communication links. At leasta plurality of base stations include respective in-channel detectors andout-of-channel detectors for detecting extraneous received signals. Thein-channel detectors analyse signals from the communication modules inthe base stations received over operational communication links. Theout-of-channel detectors include respective out-of-channel receiverelements that monitor possibly available channels alternative to therespective operational communication link channels for detectingextraneous received signals. The base station controller receivesreports of detection of extraneous received signals from the in-channeldetectors and out-of-channel detectors, registers whether channels areavailable or not for communication links, and allocates to the basestations respective target channel parameters including frequenciesavailable for operational and alternative communication links. The basestations store the respective target channel parameters that have beenchecked successfully to be available for alternative communicationlinks. The base stations change channel parameters used for therespective operational communication links as a function of the storedtarget channel parameters without further previous availability checkingof the alternative communication link channel. Examples of extraneousreceived signals include noise, interference from adjacent communicationdevices, or non-communication signals such as radar that requirereaction as well as causing noise.

Exemplary embodiments of present disclosure also includes a base stationand a base station controller for use in such a wireless communicationsystem.

Some embodiments of the present disclosure provide a base station for awireless communications system comprising one or more of the basestations, and a plurality of remotely located terminal units. The basestations and the remotely located terminal units comprise respectivecommunication modules for transmitting and receiving data overoperational wireless communication links between at least the basestations and the terminal units. The communication modules includerespective in-channel receiver elements for signals received over theoperational communication links. The base station includes at least onein-channel detector and at least one out-of-channel detector fordetecting extraneous received signals. The in-channel detector analysessignals from the communication modules in the base station received overchannels corresponding to respective operational communication links fordetecting extraneous received signals. The out-of-channel detectorincludes out-of-channel receiver elements that monitor possiblyavailable channels alternative to the respective operationalcommunication link channels for detecting extraneous received signals.The base station stores respective target channel parameters includingfrequencies available for operational and alternative communicationlinks.

If the base stations stored lists of back-up channels for use in theevent of detection of in-channel extraneous received signals withoutprior availability checking, the availability would have to be checkedbefore the base stations could use them as alternative operationalchannels. Such an availability check can take a long time, during whichthe transmissions may need to be interrupted or the interference ofreception is problematic. Monitoring in-channel and out-of-channelextraneous signals in several (or all) the base stations enables a largenumber of channels to be monitored without overloading any one basestation, and offers geographical distribution of the monitoring. The useof specific receiver elements tuned to a different channel from theoperational channel for out-of-channel monitoring can avoid interruptingtransmission and reception of data by the base station while monitoringpossible alternative channels for extraneous received signals.

The base stations may change channel parameters for the operationalcommunication links to the stored channel parameters for the alternativecommunication links on detection of in-channel extraneous receivedsignals. The base stations may change channel parameters for theoperational communication links in response to the respective in-channeldetector detecting extraneous received signals and to the base stationcontroller changing allocations of frequency for the respective basestations as a function of a report from a different base station. Thebase stations may use dynamic frequency selection techniques to changechannel parameters for the operational communication links. Thein-channel detectors and out-of-channel detectors may detect receptionof radar signals as the extraneous received signals and the dynamicfrequency selection techniques may be utilised for radar detection andavoidance.

The base stations as master units may control the channel parameters forthe communication links with linked terminal units as slave units.

The out-of-channel detectors of the base stations may perform channelavailability check procedures on the possibly available alternativechannels. The reports of detection of extraneous received signals mayinclude reports of channels that have successfully passed the channelavailability check procedures. The base station may store target channelparameters of channels that have successfully passed the channelavailability check procedures.

The wireless communication system may also include at least onedetection node having at least one receiver element that monitorsoperational and/or possibly alternative available communication linkchannels of the base stations for detecting extraneous received signals.The detection node may provide to the base stations reports of theavailability of the channels it monitors for communication links. Thedetection node may provide the reports to the base station controller,which provides the reports to the base stations. In some embodiments,the detection node functions as a base station communicating withterminal units in one operational mode, and functions in anotheroperational mode to monitor possibly alternative available communicationlink channels of the base stations for the base stations when it is notoperating as a base station itself. The detection mode may have only asingle receiver element.

If the base stations select the target channel parameters autonomously,instead of them being allocated by the base station controller, therewould be a risk of two or more base stations changing to the samealternative channel, creating race conditions. This may be undesirablein relatively complex systems, but may be acceptable in relativelysimple systems with few base stations. Some embodiments of the inventionprovide a wireless communication system comprising one or more basestations, a plurality of remotely located terminal units and at leastone detection node. The base stations and the remotely located terminalunits comprise respective communication modules for transmitting andreceiving data over operational wireless communication links between atleast the base stations and the terminal units. The communicationmodules include respective in-channel receiver elements for signalsreceived over the operational communication links. At least a pluralityof base stations include respective in-channel detectors andout-of-channel detectors for detecting extraneous received signals. Thedetection node includes an out-of-channel detector for detectingextraneous received signals. The in-channel detectors analyse signalsfrom the communication modules in the base stations received overoperational communication links. The out-of-channel detectors includerespective out-of-channel receiver elements that monitor possiblyavailable channels alternative to the respective operationalcommunication link channels for detecting extraneous received signals.The base stations and the detection node provide reports of detection ofextraneous received signals from the in-channel detectors andout-of-channel detectors. The base stations register whether channelsare available or not for communication links and store respective targetchannel parameters including frequencies available for operational andalternative communication links.

These and other aspects of the embodiments described herein will beapparent from the following description of embodiments thereof. In thisrespect, it is to be understood that the disclosed embodiments are notlimited in application to the details of construction, to thearrangements of the components and to the functioning set forth in thefollowing description or illustrated in the drawings. The exemplaryembodiments of the present disclosure are capable of other embodimentsand of being practised and carried out in various ways. Also, it is tobe understood that the phraseology and terminology employed herein arefor the purpose of description and should not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments will be described, by way ofexample only, with reference to the drawings. In the drawings, likereference numbers are used to identify like or functionally similarelements. Elements in the figures are illustrated for simplicity andclarity and have not necessarily been drawn to scale.

FIG. 1 is a schematic block diagram of elements in a wirelesscommunication system in accordance with an embodiment of the invention,given by way of example;

FIG. 2 is a schematic block diagram of an example of a warehousemanagement system including the wireless communication system of FIG. 1;

FIG. 3 is a schematic block diagram of an example of a base station inthe wireless communication system of FIG. 1 ;

FIG. 4 is a flow chart of an example of a process of starting wirelesscommunication, in-channel detection of extraneous received signals andchannel selection in the base station of FIG. 3 ;

FIG. 5 is a flow chart of an example of a process of selecting andchanging channel in the event of detection of extraneous receivedsignals in the base station of FIG. 3 ; and

FIG. 6 is a flow chart of an example of a process of out-of-channeldetection of extraneous received signals and channel availability checkin the base station of FIG. 3 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 of the drawings illustrates a communication system 100 that maybe configured to provide communications between one or more base stationcontrollers 102A to 102L, one or more base stations 104A to 104M and/orone or more network connected devices or terminal units 106A to 106N.

The base station controllers 102A to 102L may be implemented for exampleas a network manager for managing communications in a networkenvironment.

The elements that may be transmitting or receiving data may genericallybe referenced as devices, which would include at least the terminalunits 106A to 106N, base stations 104A to 104M and the base stationcontrollers 102A to 102L but may also be other elements capable oftransmitting or receiving data. Some embodiments of the inventioninclude detection nodes 108, described below.

The communication system 100 may be operable such that terminal units106A to 106N are able to communicate with one another in addition tocommunicating with one or more centralized systems, including the basestations 104A to 104M and/or the base station controllers 102A to 102L,and/or one or more network managers. The system 100 may be operable toprovide communications in a point-to-point arrangement, apoint-to-multipoint arrangement, and/or a multipoint-to-multipointarrangement.

As indicated in FIG. 1 , the communication links in the system 100 arenot necessarily established in a hierarchical fashion. Communicationlinks may be formed also between devices that perform similar functions,such as between terminal units 106A to 106N, base stations 104A to 104Mor base station controllers 102A to 102L. Certain communication linksmay be implemented using various wired technologies, in addition tolinks implemented using wireless communication technologies.

The wireless links in the system 100 may operate through a variety oftransmission media. The wireless links may communicate using, forexample, electromagnetic waves (radio waves, microwaves, infrared,light, laser, lidar, terahertz radiation), sound, or any transmissionmedium that may be utilized for wireless communications. The system mayfurther be operable in more than one transmission media.

The communication system 100 may be configured to enable communicationsby provisioning and allocating one or more communication links forcommunications by the devices. The communication system 100 may also beconfigured to utilize various technologies and/or arrangements to usethe limited spectrum bandwidth more efficiently. Each link may beprovisioned based on various factors, such as using various frequencyranges, timeslots and tiles. Each of these links may have the same ordifferent characteristics, such as bandwidth, latency, trafficcongestion or modulation scheme.

Frequencies used by various communication links may or may not beadjacent to one another, depending on the particular embodiment andconfiguration. The frequency ranges may be selected and the system 100may operate such that the system operates within various standards andmay co-exist with other users of communications frequencies, such astelevision broadcasters, mobile telephones and radar. These standardsmay vary from jurisdiction to jurisdiction. There may be regulatoryrequirements to co-exist “politely” with other users of spectrum.

The communication links may be used for transmitting or receivinginformation data and control data, and one or more communication linksmay also be utilized for emergency, monitoring or diagnostic purposes.The wireless communication system 100 may be configured to adapt tointerference or other issues by, for example, changing communicationchannels for communications, resizing communication links, applyingfilters, employing error checking, employing spatial/frequencytechniques and in particular by changing channel parameters includingfrequencies in response to detection of extraneous received signals. Thewireless communication system 100 is described herein with frequentreference to radar signals as extraneous received signals but it will beappreciated that the system 100 can also be used to detect and adapt toother extraneous received signals.

The communication links may be allocated, repurposed and/or re-sized andthe system 100 may benefit from increased flexibility in ease of use anddeployment, and when scaling up/down existing deployments. The capacityof the system may be altered by altering tile characteristics, such aspilots, forward error correction, for various reasons, such as takinginto consideration the characteristics (physical and spectral) of theenvironment. The system may be designed for indoor and/or outdoor use.

FIG. 2 illustrates an example of application of the wirelesscommunication system 100 to a warehouse facility 200 with one or morerobots including the terminal units 106A to 106N for placing objects inand picking objects from the bins. Movements of the robots may beenabled across various paths, some of which may intersect. For examplethe warehouse facility 200 may include bins arranged for example in agrid-like structure, where the robots move within the warehouse facilityto perform various tasks. Other non-robot devices may also be terminalunits, for example, a human could carry around a terminal unit forcommunication. Additional detection nodes 108 may provide reportsrelating to detection of extraneous received signals to base stations104A to 104M, as shown in FIG. 2 , or to the base station controllers102A to 102L, over suitable wired or wireless links.

The communication system in the warehouse facility 200 may be configuredto provide a bandwidth efficient radio control system forrobots/terminal units that operate on an X, Y grid of approximate 60×120meters, for example. Each grid can have many hundreds of robots andthere can be several grids in a warehouse. In one example, the system isconfigured using base stations 104A to 104M providing point tomultipoint communications using Time Division Duplex (TDD) to separatethe uplink and downlink and Time Division Multiplex (TDM) and FrequencyDivision Multiplex (FDM) to subdivide the time frequency space to allowfor a number of narrow bandwidth connections between the base stationsand the terminals/robots.

The transmitters of the base stations may use additional puncturing inthe transmit (Tx) sub frame (erasing of Tx bits to enable listening) fordetection of radar signals, noise or interference from other sources, bylistening for and detecting energy in inactive tiles in the Txsub-frame.

The warehouse facility 200 may include a robot control system 202, amaintenance/monitoring system 204, one or more warehouse managementsystems (WMS) 206, order management systems 206 and one or moreinformation management systems 208. The wireless communication links ofthe warehouse facility 200 may be based on broadband Wi-Fi, whichenables real-time or near real-time wireless communication between thebase stations 104A to 104M and the terminal units 106A to 106N of therobots.

The warehouse management system 206 may contain information such asitems required for an order, stock keeping units in the warehouse,expected/predicted orders, items missing on orders, when an order is tobe loaded on a transporter, expiry dates on items, what items are inwhich container, and whether items are fragile or big and bulky, forexample.

The robot control system 202 may be configured to control thenavigation/routing of robots, including moving from one location toanother, collision avoidance, optimization of movement paths and controlof activities to be performed, for example. The robot control system 202may be configured to send control messages to robots, receive one ormore updates from robots, and otherwise communicate with robots using areal or near-real time protocol through their terminal units 106A to106N, the base stations 104A to 104M and the base station controllers102A to 102L. The robot control system 202 may receive informationindicating robot location and availability from the base stationcontroller 102.

The maintenance/monitoring system (MMS) 204 may be configured to providemonitoring functions, including receiving alerts from therobots/terminal units 106A to 106N and the base stations 104A to 104Mand establishing connections to query the robots. The MMS 204 may alsoprovide an interface for the configuration of monitoring functions. TheMMS 204 may interact with the Robot Control System 202 to indicate whencertain robots should be recalled, or determine when an issue with thesystem has arisen, such as many clearances having been withdrawn, manypaths having failed to resolve, or a number of idle robots beyond apredetermined number.

The robots/terminal units 106A to 106N may include respective real-timecontrollers (RTC), digital signal processors (DSP) and radio modules, aswell as one or more manipulators for handling objects. The base stations104A to 104M may include respective central processor units (CPU), DSPand radio modules.

The base station controllers 102A to 102L may store master routinginformation to map the robots, the base stations, and the grids, and areconfigured to manage dynamic frequency selection and frequencyallocation of the base stations 104A to 104M. Dynamic frequencyselection (DFS), in some embodiments, may be handled by specificreceiver elements, described in more detail below, that monitor channelsfor detecting extraneous received signals, and may be part of adedicated DFS radio frequency chain.

The base stations 104A to 104M may be organized as a pool of basestations, which may then be configured to be active, on standby or tomonitor the system. Messages may be routed through the communicationsystem 100 to and from the robots/terminal units 106A to 106N, such asthose falling under IEEE wireless standard 802.11, and through fixedlinks with wired communication, for example Ethernet, to and from thebase station controllers 102A to 102L and from any detection nodes 108.The base stations 104A to 104M can each signal to the robots/terminalunits 106A to 106N linked to that base station to cease transmissionprior to the base station ceasing its own transmission, to change theoperating frequency as instructed by the base station controllers 102Ato 102L, and inform the robot/terminal units 106A to 106N of a frequencyor other channel change using a broadcast communication link.

FIG. 3 illustrates an example of a base station 300 in the wirelesscommunication system 100, which may have several similar bases stations.The system illustrated is a point to multipoint communications systemoperating in the unlicensed 5470 to 5725 MHz frequency band, but it willbe appreciated that other frequency bands may be used and that a systemcan use two or more non-adjacent frequency bands. The base station 300uses a 10 MHz bandwidth communication link allocation and may beconfigured to connect in a time division duplex (TDD) and/or a timedivision multiple access (TDMA) technique to a number of terminal unitsin a real or near real time manner.

The base station 300 has a communication module for transmitting andreceiving data. The communication module comprises two in-channelreceiver chains 302 and 304 operating in parallel for receiving datasignals over the operational communication links from antennae 306 and aswitching module 308, a transmitter chain 310 and an out-of-channelreceiver chain 312 for monitoring signals received in channels differentfrom the channels used by the receiver chains 302 and 304. A basestation may comprise only a single in-channel receiver chainrespectively, but the use of two in-channel receiver chains 302 and 304in the base station, as shown, reduces the statistical risk of theantennas for both RF chains being both located in a local null caused bydestructive interference in the multipath environment of a warehouse. Inthis example, the receiver chains 302, 304 and 312 are dual conversionsuper heterodyne receiver elements having a front end amplifier andfilter with a RF frequency of 5470 to 5725 MHz, a first down conversionto IF frequency and a final down conversion to in-phase and quadrature(IQ) baseband. The transmitter chain 310 has similar up conversionelements for generating the transmitter signal. The communication moduleof the base station 300 includes a channel allocation memory 314 thatstores parameters defining the channels used by the different chains ofthe communication module, as well as target channel parameters foralternative channels allocated by the base station controller 102,enabling a rapid change of channel in the case of detection of anextraneous received signal in the operating channel, or of a change ofoperational channel allocation. The channel allocation memory 314 pilotslocal oscillators 316 supplying the down conversion and up conversionfrequencies.

The communication module of the base station 300 includes an in-channeldetector 318 that analyses signals from the receiver chains 302 and 304received over operational communication links for detecting extraneousreceived signals. An out-of-channel detector 320 analyses basebandsignals received by the out-of-channel receiver chain 312 in channelsdifferent from the operating channels used by the receiver chains 302and 304 for detecting extraneous received signals. In this example thedetectors 318 and 320 are used for detecting radar signals and ensuringcompliance with the regulations by dynamic frequency selection (DFS),and changing the channel parameters including the frequencies to avoidthe interference with the radar transmissions. The out-of-channeldetector 320 performs channel availability check (CAC) procedures on thepossibly available alternative channels. The detectors 318 and 320 mayalso be used to detect interference by noise, or by communicationsignals from adjacent devices and avoid the interference with thereception of the wireless communication system 100 and may perform clearchannel assessment procedures on the operating and possibly availablealternative channels. The detectors 318 and 320 send signals to the basestation controller 102 forming reports of detection of extraneousreceived signals. The reports also include reports of channels that havesuccessfully passed the channel availability check and clear channelassessment procedures. Channel availability check and clear channelassessment procedures are specified in certain standards and it will beappreciated that embodiments of the invention may use proceduresspecified in the standards, and future evolutions of the standards, andmay use other procedures that are non-compliant.

The base station 300 as master unit controls the channel parameters forthe communication links with linked terminal units as slave units. Theterminal units 106A to 106N may have receiver chains, transmitterchains, antennae and switching elements similar to the correspondingelements of the base station 300, the channel parameters used by theterminal units being set by the linked base station 300. The terminalunits 106A to 106N may also detect extraneous received signals and mayalso have an out-of-channel receiver chain, an in-channel detector thatanalyses signals from the operational receiver chains and anout-of-channel detector that analyses signals received in other channelsfor detecting extraneous received signals, detection being reported tothe base station controller 102 through the linked base station 300.

FIGS. 4 to 6 illustrate, by way of example, a process ensuringcompliance with regulations governing avoidance of radar signals bydynamic frequency selection (DFS) in the wireless communication system100. FIG. 4 illustrates an example of a procedure 400 of in-channeldetection of radar signals, FIG. 5 illustrates an example of a radaravoidance procedure 500 of changing the channel parameters including thefrequencies used to avoid the interference with the radar transmissions,and FIG. 6 illustrates an example of a procedure 600 of out-of-channeldetection of radar signals. In the European Union (EU), relevantregulations from the European Telecommunications Standard Institute(ETSI) are set out in the documents EN301893, “Broadband Radio AccessNetworks (BRAN); 5 GHz high performance RLAN; Harmonized EN covering theessential requirements of article 3.2 of the R&TTE Directive”, andEN3004401, “Electromagnetic compatibility and Radio spectrum Matters(ERM); Short range devices; Radio equipment to be used in the 1 GHz to40 GHz frequency range; Part 1: Technical characteristics and testmethods”. In USA, relevant regulations are set out in the document ofthe Federal Communications Commission (FCC) “CFR47, Part 15, sections Cand E”. These documents set out regulatory requirements for both normaloperation and use, referred to as field operation, and for testing inspecified configurations and conditions, referred to as test operation.The operation of the wireless communication system is described belowwith reference to field operation, the test operation being similar,apart from differences caused by the specified test configurations andconditions. The regulations define channel numbers (n=5482.5+n*10) MHz,where n is an integer from 0 to 23. The channels are divided into twosets: set1 is channel numbers 0 to 11 and 18 to 23 and set2 is channelnumbers 12 to 17. The operational requirements for set2 are morestringent than for set1.

Under EU regulations, on power up a base station (BS) must check apotential channel by the channel availability check (CAC) procedure for60 seconds minimum if the channel is in set1 and 600 seconds if thechannel is in set2. Set1 channels are to be checked first. If radar isnot detected in the channel, this channel becomes the operating channeland the in-channel detector 318 continues to monitor continuously forradar detection. If radar is detected on the operating channel thewireless communication system 100 is to switch channel, if one isavailable. If none is available then transmission in that channel is tocease within a specified maximum time and another channel is to bechecked using CAC. Any channels that are found to have radar presentmust not be used for 30 minutes by any of the BSs or the terminal unitsin the wireless communication system 100.

The out-of-channel detector 320 monitors all channels other than theoperating channel on a cyclical basis, starting with channels only fromset1, and for a minimum duration of 6 minutes for each channel. Afterchecking set1 channels, if the out-of-channel detector 320 monitors set2channels it checks each set2 channel for a minimum duration of 1 hour.

The base station controller (BSC) 102 receives signals reporting theresults of the CACs from all the base stations, including any resultsfrom the terminal units. The BSC 102 registers all channels that havebeen checked for more than the minimum duration (white list) and withoutany BS detecting a radar signal. The BSC 102 also registers all channelsthat any BS has detected radar in (black list). The BSC 102 allocateschannels only from the white list to the base stations for the operatingcommunication links and also for the channels to be monitored by theout-of-channel detector 320 in this example. In another example ofoperation of an embodiment of the invention, the BS 104A to 104M select,at least in part autonomously, the channels to be monitored by theout-of-channel detector 320. Detection of radar in any channel in thewhite list transfers the channel immediately to the black list and theBSC 102 allocates a change to a new channel from the white list to anyBS using the incriminated channel. The allocations of channels areregistered in the channel allocation memory 314 of each base station,for immediate use without needing to perform the CAC procedure. In oneembodiment of the invention, the base stations cease transmitting whenradar is detected if no new channel is allocated by the BSC 102 asavailable or stored in its white list. The regulations also provide forbase station operation when not connected to a base station controller,in which circumstances the base stations keep their own white lists andblack lists, with updating by communication directly between thedifferent base stations in another embodiment of the invention.

The process 400 of in-channel detection of radar signals starts at 402with power up of the base station. At 404, the process 400 branches andif the communication system 100 is being tested the system follows theprocedure 406 set out in the relevant regulations for testing. When thesystem is being used in field operation, the process 400 branches againat 408 and is described below if the system is operating according to EUregulations, the process 400 following generally similar procedures 410with different parameters for other regulations.

Under EU regulations at 412 the base stations (BS) start the channelavailability check (CAC) procedure by setting thresholds for minimumlevels of detection of radar signals, with the BS transmitters OFF, thethresholds being set by the BSC 102, when the BSs are connected to theBSC, in normal field operation. At 414, the in-channel detectors 318perform CAC on a channel allocated by the BSC 102 from channel set1, theBSC 102 removing that channel from the list of channels from set1 thatcan be allocated as the operating channel. The in-channel detectors 318of the BSs check the channel for radar signals at 416 during 60 secsminimum. At 418, if a radar signal is detected in the channel, thedetector sends a report signal to the BSC 102 and the BSC 102 includesthe channel at 420 in the black list not to be used for at least 30minutes by any of the BSs or the terminal units in the wirelesscommunication system 100. At 422 the process branches and if there areany channels left in set1, the BSC 102 allocates another channel to bechecked and the process 400 reverts to performing CAC on the new channelat 414. If there are no channels left in set1, the process 400 raises analert at 424, to bring to the attention of the human operators/supportstaff of the system that there is an issue, and then checks set2channels. At 426, the in-channel detectors 318 perform CAC on a channelallocated by the BSC 102 from channel set2, the BSC 102 removing thatchannel from the list of channels from set2 that can be allocated as theoperating channel. The in-channel detectors 318 of the BSs check thechannel for radar signals at 428 during 600 secs minimum. At 430, if aradar signal is detected in the channel, the detector sends a reportsignal to the BSC 102 and the BSC 102 includes the channel at 432 in theblack list not to be used for at least 30 minutes by any of the BSs orthe terminal units in the wireless communication system 100. At 434 theprocess branches and if there are any channels left in set2, the BSC 102allocates another channel to be checked and the process 400 reverts toperforming CAC on the new channel at 426. If there are no channels leftin set2, the process 400 raises an alert at 436. The process 400branches at 438: if there are any channels that were on the black listthat have completed a duration of 30 mins without further detection ofradar signals, they are re-instated in set1 or set2 at 440 and theprocess 400 reverts to the CAC procedure at 412. If no channels thatwere on the black list have completed a duration of 30 mins withoutfurther detection of radar signals, the base station that has beenprevented from transmitting on its operating channel reverts to the CACprocedure at 412 without transmitting until a channel has becomeavailable and it has been allocated a channel from the white list.

If at 418 or 430 no radar signal is detected in the channel, thedetector sends a report signal to the BSC 102 and the BSC 102 allocatesthe channel to the base station and linked terminal units as newoperating channel and at 442 the base station and linked terminal unitstune their transmitters and receivers to the new channel parameters. Thereaction of the wireless communication system 100 to switch channelsmust conform to maximum timings specified in the relevant regulations.At 444, the out-of-channel detector 320 starts monitoring all channelsother than the operating channel on a cyclical basis, according to theprocess 600 described below with reference to FIG. 6 . The in-channeldetector 318 continues to monitor continuously for radar signaldetection at 446 and can monitor for radar signals even in slots whereit is transmitting itself, during tiles which it is not using. If energyis found at 448 corresponding to a radar signal, the detector sends areport signal to the BSC 102 and the wireless communication system 100starts the radar avoidance procedure 500 illustrated in FIG. 5 .

The radar avoidance procedure 500 starts by the base stations and theBSC 102 including the channel at 502 in the black list not to be usedfor at least 30 minutes by any of the BSs or the terminal units in thewireless communication system 100. This is performed by the BSC 102 ifat 504 the connections of the base stations to the BSC 102 areestablished. However certain regulations specify test procedures withthe base stations disconnected from the BSC. If at 504 the base stationsare connected to the BSC 102, and if at 506 a backup channel isavailable on the white list, the BSC 102 chooses at 508 a channel toallocate to the base station at 510. If at 506 no backup channel isavailable on the white list, the base station that has been preventedfrom transmitting on its operating channel reverts to the CAC procedureat 412 (FIG. 4 ) without transmitting until a channel has becomeavailable.

If at 504 the base stations are not connected to the BSC 102, theprocedure relies on white and black lists registered in the basestations themselves on detection by themselves or by linked terminalunits or by other base stations through connections directly between thebase stations. If at 512 the out-of-channel detectors 320 haveidentified no backup channel available, or if at 514 a backup channelwould be available but is still on 30 min. timeout, the base stationthat has been prevented from transmitting on its operating channelreverts to the CAC procedure at 412 without transmitting until a channelhas become available. If a channel is allocated to the base station at510, the base station signals to the linked terminal units to changechannel and then stops its transmission. At 516 the base station checkswhether the linked terminal units have reconnected to the new channelwithin less than 10 secs. If so, at 518 the base station and linkedterminal units tune their transmitters and receivers to the new channelparameters at 442 (FIG. 4 ). If at 516 one or more linked terminal unitshave not reconnected to the new channel within less than 10 secs, analert is raised at 520. The alert is raised to ease operation of thesystem and to make the operations staff aware of an issue. Now that theBS has moved to a new channel, the terminal units will not transmituntil they have re-tuned their receivers and successfully decodedbroadcast traffic from the BS, sometimes referred to as listen beforespeak.

The procedure 600 of out-of-channel detection of radar signals starts at602 with the BSC 102 (if connected, otherwise the base station chooses awhite list channel) allocating a channel from set1 that is differentfrom the operating channel of that base station, is not already on thewhite list and is not subject to 30 min. timeout. If at 604 no channelfrom set1 with these criteria exists, a channel from set2 is allocatedat 606. The radar receiver 312 and out-of-channel detector 320 are tunedto the allocated channel at 608 and start detection and analysis. Allthe receiver sub-frames in the allocated channel are scanned at 610 forradar signals (or interference), since no data is being transmitted inthis channel. If energy is found at 612, the detector sends a reportsignal to the BSC 102 and the BSC 102 includes the channel at 614 in theblack list not to be used for at least 30 minutes by any of the BSs orthe terminal units in the wireless communication system 100 and theprocedure 600 reverts to 602 with the BSC 102 allocating a channel. Ifat 616 the channel monitored by the out-of-channel detector 320 is fromset1, and if the channel has been monitored for 6 mins, the detector 320sends a report signal to the BSC 102 and the BSC 102 includes thechannel at 620 in the white list. If at 622 the channel monitored by theout-of-channel detector 320 is from set2, and if the channel has beenmonitored for 1 hour, the detector 320 sends a report signal to the BSC102 and the BSC 102 includes the channel at 620 in the white list.Otherwise, the detector 320 continues monitoring the channel at 610.

The procedures are described above with reference to detection of radarsignals. It will be appreciated that embodiments of the invention mayreact to detection of other extraneous signals, instead of or inaddition to radar signals. The reaction may depend on the type of signaldetected.

The invention may be implemented at least partially in a computerprogram for running on a computer system, at least including codeportions for performing steps of a method according to the inventionwhen run on a programmable apparatus, such as a computer system orenabling a programmable apparatus to perform functions of a device orsystem according to the invention.

A computer program is a list of instructions such as a particularapplication program and/or an operating system. The computer program mayfor instance include one or more of: a subroutine, a function, aprocedure, an object method, an object implementation, an executableapplication, an applet, a servlet, a source code, an object code, ashared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer system.

The computer program may be stored internally on computer readablestorage medium or transmitted to the computer system via a computerreadable transmission medium. All or some of the computer program may beprovided on computer readable media permanently, removably or remotelycoupled to an information processing system. The computer readable mediamay include, for example and without limitation, any number of thefollowing: magnetic storage media including disk and tape storage media;optical storage media such as compact disk media (e.g., CD-ROM, CD-R,etc.) and digital video disk storage media; non-volatile memory storagemedia including semiconductor-based memory units such as FLASH memory,EEPROM, EPROM, ROM; ferromagnetic digital memories; MRAM; volatilestorage media including registers, buffers or caches, main memory, RAM,etc.; and data transmission media including computer networks,point-to-point telecommunication equipment, and carrier wavetransmission media, just to name a few.

A computer process typically includes an executing (running) program orportion of a program, current program values and state information, andthe resources used by the operating system to manage the execution ofthe process. An operating system (OS) is the software that manages thesharing of the resources of a computer and provides programmers with aninterface used to access those resources. An operating system processessystem data and user input, and responds by allocating and managingtasks and internal system resources as a service to users and programsof the system.

The computer system may for instance include at least one processingunit, associated memory and a number of input/output (I/O) devices. Whenexecuting the computer program, the computer system processesinformation according to the computer program and produces resultantoutput information via I/O devices.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims.

The connections as discussed herein may be any type of connectionsuitable to transfer signals from or to the respective nodes, units ordevices, for example via intermediate devices. Accordingly, unlessimplied or stated otherwise, the connections may for example be directconnections or indirect connections. The connections may be illustratedor described in reference to being a single connection, a plurality ofconnections, unidirectional connections, or bidirectional connections.However, different embodiments may vary the implementation of theconnections. For example, separate unidirectional connections may beused rather than bidirectional connections and vice versa. Also,plurality of connections may be replaced with a single connections thattransfers multiple signals serially or in a time multiplexed manner.Likewise, single connections carrying multiple signals may be separatedout into various different connections carrying subsets of thesesignals. Therefore, many options exist for transferring signals.

Those skilled in the art will recognize that the boundaries betweenlogic blocks are merely illustrative and that alternative embodimentsmay merge logic blocks or circuit elements or impose an alternatedecomposition of functionality upon various logic blocks or circuitelements. Thus, it is to be understood that the architectures depictedherein are merely exemplary, and that in fact many other architecturescan be implemented which achieve the same functionality.

Any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediate components. Likewise, any two componentsso associated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations merely illustrative. The multipleoperations may be combined into a single operation, a single operationmay be distributed in additional operations and operations may beexecuted at least partially overlapping in time. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code, such asmainframes, minicomputers, servers, workstations, personal computers,notepads, personal digital assistants, electronic games, automotive andother embedded systems, cell phones and various other wireless devices,commonly denoted in this application as ‘computer systems’.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the terms “a” or “an,” as used herein, are definedas one, or more than one. Also, the use of introductory phrases such as“at least one” and “one or more” in the claims should not be construedto imply that the introduction of another claim element by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim element to inventions containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles. The mere fact thatcertain measures are recited in mutually different claims does notindicate that a combination of these measures cannot be used toadvantage.

The invention claimed is:
 1. A wireless communication system comprising:a plurality of base stations; and a plurality of remotely locatedterminal units; the base stations and the remotely located terminalunits having respective communication modules configured fortransmitting and receiving data over operational wireless communicationlinks between at least the base stations and the terminal units, thecommunication modules including respective in-channel receiver elementsfor signals received over the operational communication links; and atleast one base station controller configured to control channelparameters used by the base stations for the respective communicationlinks, the channel parameters including allocations of frequencies foruse in the communication links, wherein at least a plurality of basestations include respective in-channel detectors and out-of-channeldetectors for detecting extraneous received signals, wherein thein-channel detectors are configured to analyse signals from thecommunication modules in the base stations received over the operationalcommunication links, wherein the out-of-channel detectors includerespective out-of-channel receiver elements configured to monitorcandidate available channels alternative to the operationalcommunication links for detecting extraneous received signals, whereinthe base station controller is configured to: receive reports ofdetection of extraneous received signals from the in-channel detectorsand out-of-channel detectors; register whether channels are available ornot for communication links; and allocate to the base stationsrespective target channel frequencies available for operational andalternative communication links, wherein the base stations areconfigured to store the respective target channel frequencies that havebeen checked successfully to be available for operational andalternative communication links, and wherein the base stations areconfigured to change channel parameters used for the respectiveoperational communication links to the allocated stored target channelfrequencies without additional availability checking of the alternativecommunication links.
 2. A wireless communications system according toclaim 1, wherein the base stations are configured to change channelparameters for the operational communication links to the stored channelfrequencies for the alternative communication links in response todetection of in-channel extraneous received signals.
 3. A wirelesscommunications system according to claim 2, wherein the base stationsare configured to change channel parameters for the operationalcommunication links in response to the respective in-channel detectordetecting extraneous received signals and to the base station controllerchanging allocations of frequency for the respective base stations as afunction of a report from a different base station.
 4. A wirelesscommunication system according to claim 2, wherein the base stations areconfigured to use dynamic frequency selection techniques to changechannel parameters for the operational communication links.
 5. Awireless communications system according to claim 4, wherein thein-channel detectors and out-of-channel detectors are configured todetect reception of radar signals as the extraneous received signals andthe dynamic frequency selection techniques are utilised for radardetection and avoidance.
 6. A wireless communications system accordingto claim 1, wherein the base stations are configured as master units tocontrol the channel parameters for the communication links with linkedterminal units as slave units.
 7. A wireless communications systemaccording to claim 1, wherein the out-of-channel detectors of the basestations are configured to perform channel availability check procedureson the possibly available alternative channels, and the reports ofdetection of extraneous received signals include reports of channelsthat have successfully passed the channel availability check procedures.8. A wireless communications system according to claim 1, comprising: atleast one detection node having at least one receiver element that isconfigured to monitor operational and/or possibly alternative availablecommunication link channels of the base stations for detectingextraneous received signals, and that is configured to provide to thebase stations reports of the availability of the channels it monitorsfor communication links.
 9. A wireless communications system accordingto claim 8, wherein the detection node is configured to provide thereports to the base station controller, which provides the reports tothe base stations.
 10. A wireless communications system according toclaim 8, wherein the detection node functions as a base stationcommunicating with terminal units in one operational mode, and functionsin another operational mode to monitor possibly alternative availablecommunication link channels of the base stations for the base stationswhen it is not operating as a base station itself.
 11. A base stationconfigured for use in a wireless communications system, wherein thewireless communications system includes: a plurality of the basestations; and a plurality of remotely located terminal units; the basestations and the remotely located terminal units having respectivecommunication modules for transmitting and receiving data overoperational wireless communication links between at least the basestations and the terminal units, the communication modules includingrespective in-channel receiver elements for signals received over theoperational communication links; and at least one base stationcontroller configured to control channel parameters used by the basestations for the respective communication links, the channel parametersincluding allocations of frequencies for use in the communication links;the base station comprising: at least one in-channel detector and atleast one out-of-channel detector for detecting extraneous receivedsignals, wherein the in-channel detector is configured to analysesignals from the communication modules in the base station received overchannels corresponding to respective operational communication links fordetecting extraneous received signals, wherein the out-of-channeldetector includes out-of-channel receiver elements that are configuredto monitor candidate available channels alternative to the respectiveoperational communication link channels for detecting the extraneousreceived signals, and wherein the base station is configured to: send tothe base station controller reports of detection of extraneous receivedsignals from the in-channel detectors and out-of-channel detectors;register whether channels are available or not for communication links;allocate to the base station target channel parameters includingfrequencies available for operational and alternative communicationlinks; store the respective allocated target channel frequencies thathave been checked successfully to be available for alternativecommunication links; and change channel parameters used for therespective operational communication links to the allocated storedtarget channel frequencies without additional availability checking ofthe alternative communication links.
 12. A base station according toclaim 11, wherein the base station is configured to change channelparameters for the operational communication links to the stored channelparameters for the alternative communication links in response todetection of in-channel extraneous received signals.
 13. A base stationaccording to claim 11, wherein the base station is configured to changechannel parameters for the operational communication links in responseto the in-channel detector detecting extraneous received signals and tothe base station controller changing allocations of frequency for therespective base stations as a function of a report from a different basestation.
 14. A base station according to claim 12, wherein the basestation is configured to use dynamic frequency selection techniques tochange channel parameters for the operational communication links.
 15. Abase station according to claim 14, wherein the in-channel detector andout-of-channel detector are configured to detect reception of radarsignals as the extraneous received signals and the dynamic frequencyselection techniques are utilised for radar detection and avoidance. 16.A base station according to claim 11, wherein the base station isconfigured as a master unit to control the channel parameters for thecommunication links with linked terminal units as slave units.
 17. Abase station according to claim 11, wherein the out-of-channel detectoris configured to perform channel availability check procedures on thecandidate available alternative channels, and the reports of detectionof extraneous received signals include reports of channels that havesuccessfully passed the channel availability check procedures.